The present invention relates to a process for preparing 5,6-dihydro-4-hydroxy-(S)-6-methyl-thieno-[2,3-b]thiopyran-7,7-dioxide having the formula (II): ##STR3##
The above-mentioned thienothiopyran derivative (II) of the invention is a useful synthetic intermediate which can be converted by an organic chemical method which is conventionally used, into the drug for glaucoma MK-507 having the formula (III): ##STR4## (Fortoshuritte der Ophthalmologie 88, p513, 1991).
Therefore, it has been desired to .develop a process for preparing the above-mentioned thienothiopyran derivative having the formula (II) which enables efficient production on an industrial scale.
However, any satisfiable process has not been known until now. No document describes a process for preparing 5,6-dihydro-4-hydroxy-(S)-6-methyl-thieno-[2,3-b]thiopyran-7,7-dioxide having the formula (II), which comprises reducing 5,6-dihydro-4-oxo-(S)-6-methyl-thieno-[2,3-b]thiopyran-7,7-dioxide having the formula (I): ##STR5## with a microorganism.
The synthesis method described in Japanese Unexamined Patent Publication No. 100174/1989 has been known as the process for preparing the above-mentioned thienothiopyran derivative (III). However, a process comprising the step wherein the thienothiopyran derivative (I) is reduced with a microorganism to give the thienothiopyran derivative (II), is not known.
An object of the invention is to provide a simple and efficient process for preparing the thienothiopyran derivative (II) which can be industrially used.
This and the other objects of the present invention will become apparent from the description hereinafter.